Vikings raided and plundered Ireland for much of the ninth century, eventually establishing two outposts. The fates of those two settlements couldn't be more different. The Dúbh Linn outpost became, well, Dublin, but the other was lost forever... until now.

According to the fifteenth century history work The Annals of Ulster, the Vikings started wreaking havoc on Ireland in 795, but eventually they settled down enough to found a couple outputs, Dúbh Linn and Linn Duchaill. The ultimate fate of Linn Duchaill had been an archaeological mystery for centuries, until last week's announcement that the settlement had been found 45 miles north of Dublin in the village of Annagassan.

The people of Annagassan have long possessed a rich oral tradition of Viking raids and a nearby lost settlement. This story has been backed up by occasional small discoveries, like ancient handcuffs the Vikings would have used on their slaves. All this was enough to convince local filmmaker Ruth Cassidy to enlist the help of archaeologist friend Mark Clinton to find the lost outpost.

The search began in 2005, and it wasn't until 2007 - when they were nearly at the point of giving up - that they finally found something worthwhile. They discovered a flat area a mile or so upriver from Annagassan that seemed ideal for shipbuilding, which meant it was the perfect place for a medieval outpost. They enlisted the help of a geophysicist, who found a bunch of defensive ditches, all about fifteen feet deep.

The fact that these ditches were arranged in straight lines didn't fit with the more circular patterns of the ring forts built by medieval Irishmen. Nor was there any evidence of a Norman castle here. That meant this had to be the work of Vikings, and subsequent excavations turned up an amazing 200 artifacts in just three short weeks. The settlement was definitely a big one, and there's evidence of shipbuilding, carpentry, smelting, and even an artificial island that would have been used for defense against the locals.

Archaeologists are hopeful that this really is Linn Duchaill, although until artifacts are dated it won't be possible to know for sure. As Viking expert Peter Pentz explains, this find could provide invaluable insight into a ninth century Viking outpost, not to mention prove the reliability of The Annals of Ulster:

"If the settlement found can be identified as Linn Duchaill, its value for linking archaeology to the written sources is very important. In addition, it appears that the site is almost untouched by later activity, unlike those of Dublin-some longphorts developed into urban settlements-and thus it might provide important knowledge of this particular type of settlement."

Of course, this does leave one question - why did Dúbh Linn eventually become Ireland's most important city, while Linn Duchaill was lost to time? We don't know for sure, but archaeologists suspect it all has to do with access to the sea. Dublin enjoys pretty much constant access to the ocean, which provided Vikings with an escape hatch if they were ever under attack. Linn Duchaill, on the other hand, is blocked off from the sea for hours each day because of shifting tides, which may mean the Vikings were eventually surrounded and killed by the indigenous Irish with no chance of escape.